1. Field of the Invention
The invention relates to towers for cooling heated fluids such as water and, more particularly, to a cooling tower operating on the induced draft principle and employing a unitary shell fabricated from an inexpensive plastics material.
2. Description of the Prior Art
Many industrial applications require that heated fluids such as water be cooled down before the fluids can be used for other purposes. The discussion that follows will refer to water as the fluid being cooled although it should be understood that the invention can have applicability to other fluids.
In order to cool heated water, a commonly used method is to bring it into direct contact with ambient air impelled by one or more fans, in a so-called mechanical draft cooling tower. These cooling towers have been divided into two general types. The first type operates on the forced draft principle whereby a fan located at ground level pumps air under pressure into the tower through ductwork. The pressurized air, upon being brought into contact with hot water, will cool the water. The second type of cooling tower is known as an induced draft tower whereby a fan is connected to the tower and draws air through the tower, thereby "inducing" a flow of cooling air through the tower. In most induced draft cooling towers, the fan is positioned directly atop the tower, thereby eliminating the need for ductwork connecting the tower outlet to the fan inlet. In either a forced draft cooling tower or an induced draft cooling tower, the flow of water through the tower may be opposite to that of the airflow (counterflow), or it may be across the direction of airflow (crossflow). In either case, a heat exchanger in the form of a block of cellular packing is disposed within the tower to provide maximum contact between the air and the water.
Forced draft cooling towers have the advantage that the fan and its associated ductwork do not need to be supported by the tower structure itself. The fan and associated ductwork often are quite heavy and it is advantageous to be able to use a less expensive, relatively weak tower. Although the structural requirements of forced draft cooling towers are favorable, the cooling efficiency of forced draft cooling towers is not as great. This is because the air usually is directed into the tower at only one location. It is very difficult, if not impossible, to design the interior of the tower to produce uniform airflow. Accordingly, the efficiency of a forced draft cooling tower is not as great as desired.
Induced draft cooling towers, on the other hand, are more efficient than forced draft cooling towers because air can be drawn into the lower portion of the tower through a plurality of inlets equidistantly spaced about the circumference of the tower. A very even airflow pattern will result. Unfortunately, as has been indicated already, the strength of the tower must be increased in order to accommodate the extra weight of the fan. Moreover, the added cross-sectional area of the fan located atop the tower makes it more difficult for the tower to withstand windstorms. Yet an additional consideration is that if many air inlets are provided, the remaining portion of the tower intermediate the inlets may be loaded too heavily; that is, the greater the number of air inlets, the weaker the base of the tower.
Prior induced draft cooling towers, in order to attain adequate structural strength, have required either that the tower be manufactured from a very strong material such as steel or that the tower employ external steel reinforcing members. The most important drawback of a steel construction is that is eventually will rust, thereby significantly shortening the life of the tower. In addition, steel construction is expensive, difficult to transport, difficult to assemble on-site and requires greater structural support in the surface on which the tower is disposed. Even if a lightweight, rust-free material such as a plastics material is employed for the tower, it has been found necessary to use a strong, expensive plastics material such as fiberglass reinforced polyester (FRP), and, in addition, to augment the FRP with external steel supports. The resultant construction, although strong, also is very expensive.
Desirably, an induced draft cooling tower would be manufactured of an inexpensive, rust-free plastics material such as polyethylene, and, at the same time, would avoid the need for supplementary structural members. It also would be desirable to provide an induced draft cooling tower having many flat surfaces near its lower end for easy fabrication of air inlets, for easy attachment of various plumbing fixtures, and for easy attachment of anchor lugs connected to a concrete pad or other supporting base. It also would be desirable to support the cellular packing and other components within the tower with a minimum number of attachment fittings, not only to avoid the need for rust-susceptible elements, but also to conserve expense and weight.